Electrophotographic materials and methods employing photoconductive resinous charge transfer complexes



United States Patent Office 3,408,187 Patented Oct. 29, 1968 3,408,187ELECTROPHOTOGRAPHIC MATERIALS AND METHGDS EMPLOYING PHOTOCONDUC- TIVERESINOUS CHARGE TRANSFER COMPLEXES Joseph Mammino, Penr'ield, N.Y.,assignor to Xerox Corporation, Rochester, N.Y., a corporation of NewYork No Drawing. Filed Jan. 24, 1966, Ser. No. 522,393 24 Claims. (Cl.961.5)

ABSTRACT OF THE DISCLOSURE Photoconductive materials are prepared fromaromatic silicone resins and Lewis acids. The materials are chargetransfer complexes. The photoconductive materials are used to makeelectrophotographic plates. Methods of using the plates are alsodisclosed.

This invention relates to photoconductive materials, and moreparticularly, to their use in electrophotography.

It is known that images may be formed and developed on the surface ofcertain photoconductive materials by electrostatic means. The basicxerographic process, as taught by Carlson in US. Patent 2,297,691,involves uniformly charging a photoconductive insulating layer and thenexposing the layer to a light-and-shadow image which dissipates thecharge on the areas of the layer which are exposed to light. Theelectrostatic latent image formed on the layer corresponds to theconfiguration of the light-and-shadow image. This image is renderedvisible by depositing on the image layer a finely divided developingmaterial comprising an electroscopic marking material called a toner.The powder developing material will normally be attracted to thoseportions of the layer which retain a charge, thereby forming a powderimage corresponding to the latent electrostatic image. This powder imagemay be transferred to paper or other receiving surfaces. The paper thenwill bear the powder image which may subsequently be made permanent byheating or other suitable fixing means. The above general process isalso described in US. Patents, 2,357,809; 2,891,011 and 3,079,342. i

That various photoconductive insulating materials ma be used in makingelectrophotographic plates is known. Suitable photoconductive insulatingmaterials such as anthracene, sulfur, selenium or mixtures thereof, havebeen disclosed by Carlson in US. Patent 2,297,691. These materialsgenerally have sensitivity in the blue or near ultraviolet range, andall but selenium have a further limitation of being only slightly lightsensitive. For this reason, selenium has been the most commerciallyaccepted material for use in electrophotographic plates.

Vitreous selenium however, while desirable in most aspects, suffers fromserious limitations in that its spectral response is somewhat limited tothe'ultraviolet, blue and green regions of the spectrum and thepreparation of vitreous selenium plates requires costly and complexprocedures, such as vacuum evaporation. Also, selenium plates requirethe use of a separate conductive substrate layer, preferably with anadditional barrier layer deposited thereon before deposition of theselenium photoconductor. Because of these economic and commercialconsiderations, there have been many recent efforts towards developingphotoconductive insulating materials other than selenium for use inelectrographic plates.

It has been proposed that various two-component materials be used inphotoconductive insulating layers used in electrophotographic plates.For example, the use of inorganic photoconductive pigments dispersed insuitable binder materials to form photoconductive insulating layers isknown. It has further been demonstrated that organic photoconductivedyes and a wide variety of polycyclic compounds may be used togetherwith suitable resin materials to form photoconductive insulating layersuseful in binder-type plates. In each of these two systems, it isnecessary that at least one original component used to prepare thephotoconductive insulating layer be, itself, a photoconductive material.

In a third type plate, inherently photoconductive polymers are used;frequently in combination with sensitizing dyes or Lewis acids to formphotoconductive insulating layers. Again, in these plates at least onephotoconductive component is necessary in the formation of the layer.While the concept of sensitizing photoconductors is, itself,commercially useful, it does have the drawback of being limited to onlythose materials already having substantial photoconductivity.

The above discussed three types of known plates are further described inUS. Patents 3,097,095; 3,113,022; 3,041,165; 3,126,281; 3,073,861;3,072,479; 2,999,750; Canadian Patent 644,167 and German Patent1,068,115.

The polymeric and binder-type organic photoconductor plates of the priorart generally have the inherent disadvantages of high cost ofmanufacture, brittleness, and poor adhesion to supporting substrates. Anumber of these photoconductive insulating layers have low temperaturedistortion properties which make them undesirable in an automaticelectrophotographic apparatus which often includes powerful lamps andthermal fusing devices which tend to heat the xerographic plate. Also,the choice of physical properties has been limited by the necessity ofusing only inherently photoconductive materials.

Inorganic pigment-binder plates are limited in usefulness because theyare often opaque and are thus limited to use in systems where lighttransmission is not required. Inorganic pigment-binder plates have thefurther disadvantage of being nonreusable due to high fatigue and roughsurfaces which make cleaning difiicult. Still another disadvantage isthat the materials used have been limited to those having inherentphotoconductive insulating properties.

It is, therefore, an object of this invention to provide aphotoconductive insulating material suitable for use inelectrophotographic plates devoid of the above-noted disadvantages.

Another object of this invention is to provide an economical method forthe preparation of photoconductive insulating materials wherein none ofthe required components is by itself substantially photoconductive.

Another object of this invention is to provide a photoconductiveinsulating material suitable for use in electrophotographic plates inboth single use and reusable systems.

Yet still another object is to provide a photoconductive insulatinglayer for an electrophotographic plate which is substantially resistantto abrasion and has a relatively high distortion temperature.

Yet, a further object of this invention is to provide anelectrophotographic plate having a wide range of useful physicalproperties.

A still further object of this invention is to provide photoconductiveinsulating layers which may be cast into the photoconductive insulatinglayer of xerographic plate which are easily coated on a desiredsubstrate or combined with a conductive layer. 1 I

(A) A suitable Lewis Acid with (B) An aromatic silicon resin having thegeneral forwherein each R is selected from the group consisting of aryland alkyl radicals; at least one R being aryl; and n is a positiveinteger, at least 2.

It should be noted that neither of the above two components, (A) and (B)used to make the photoconductor of this invention is by itselfphotoconductive; rather, they are each nonphotoconductive.

After the above substantially nonphotoconductive Lewis acid is mixed orotherwise complexed with said substantially nonphotoconductive resinousmaterial, a highly desirable photoconductive insulating material isobtained which may be either cast as a self-supporting layer or may bedeposited on a suitable supporting substrate. Any other suitable methodof preparing a photoconductive plate from the above photoconductivematerial may be used.

It has been found by the present invention that electron acceptorcomplexing may be used to render inherently nonphotoconductive electrondonor type insulators photoconductive. This greatly increases the rangeof useful materials for electrophotography.

A Lewis Acid is any electron acceptor relative to other materialspresent in the system. A Lewis Acid will tend to accept electronsfurnished by an electron donor (or Lewis base) in the process of forminga chemical compound or, in the present invention, a charge transfercomplex.

A Lewis Acid is defined for the purposes of this invention as anyelectron accepting material relative to the polymer to which it iscomplexed.

A charge-transfer complex may be defined as a molecular complex betweensubstantially neutral electron donor and acceptor molecules,characterized by the fact that photoexcitation produces internalelectron transfer to yield a temporary excited state in which the donoris more positive and the acceptor more negative than in the groundstate.

It is believed that the donor-type insulating resins of the presentinvention are rendered photoconductive by the formation of chargetransfer complexes with electron acceptors or Lewis Acids and that thesecomplexes, once formed, constitute the photoconductive elements of theplates.

Broadly speaking, charge transfer complexes are loose associationscontaining electron donors and acceptors, frequently in stoichiometricratios, which are characterized as follows:

(A) Donor-acceptor interaction is weak in the neutral ground state, i.e.neither donor nor acceptor is appreciably perturbed by the other in theabsence of photoexcitation.

(B) Donor-acceptor interaction is relatively strong in the photoexcitedstate, i.e. the components are at least partially ionized byphotoexcitation.

(C) When the complex is formed, one or more new absorption bands appearin the near ultraviolet or visible region (wave lengths between3200-7500 angstrom units) which are present in neither donor alone noracceptor alone, but which are instead a property of the donoracceptorcomplex.

Both the intrinsic absorption bands of the donor and the charge transferbands of the complex may be used to excite photoconductivity.

Photoconductive insulator for the purposes of this invention is definedwith reference to the practical application in electrophotographicimaging. It is generally considered that any insulator may be renderedphotoconductive through excitation by sutficiently intense radiation ofsufficiently short wave-lengths. This statement applies generally toinorganic as well as to organic materials, including the inert binderresins used in binder plates, and the electron acceptor type activatorsand aromatic resins used in the present invention. However, the shortwavelength radiation sensitivity is not useful in practical imagingsystems because sufficiently intense sources of wavelengths below 3200angstrom units are not available, because such radiation is damaging tothe human eye and because this radiation is absorbed by glass opticalsystems. Accordingly, for the purposes of this application, the termphotoconductive insulator includes only those materials which may becharacterized as follows:

(1) They may be formed into continuous films which are capable ofretaining an electrostatic charge in the absence of actinic radiation.

(2) These films are sufficiently sensitive to illumination ofwavelengths longer than 3200 angstrom units to be discharged by at leastone half by a total flux of at most 10 quanta/cm. of absorbed radiation.

This definition excludes the resins and Lewis Acids of our disclosurewhen used individually from the class of photoconductive insulators.

The aromatic silicone resins used in the present invention may beprepared in any conventional manner. For example, any of the synthesisdescribed in Silicones by R. N. Meals and F. M. Lewis, ReinholdPublishing Corp, New York (1959), may be used.

Any suitable aromatic silicone resin may be used in the presentinvention. Optimum sensitivity is obtained when usingphenyltrichlorosilane, diphenyldimethoxy sil'ane,methylphenyldiethoxysilane and dimethylphenyldichlorosilane in thepreparation of the resin, therefore, these silane compounds arepreferred. Other typical aromatic silicone resins include those preparedfrom diphenyltrichlorosilane, dinaphthylsilanediol,anthracenetrichlorosilane, biphenylenetrichlorosilane,fluorenetrichlorosilane and 9,9-dicarbazalolyldichlorosilane. The resinmay be cross-linked for greater durability, if desired.

Any suitable Lewis Acid can be complexed withthe above-noted siliconeresins to form the desired photoconductive material. While the mechanismof the complex chemical interaction involved in the present process isnot completely understood, it is believed that a charge transfer complexis formed having absorption band characteristics of neither of the twocomponents considered individually. The mixture of the twononphotoconductive components seems tohave a synergistic effect which ismuch greater than additive.

Best results are obtained when using these preferred Lewis Acids:2,4,7-trinitro-9-fluorenone, tetrachlorophthalic anhydride, chloranil,picric acid, benz(a) anthracene- 7, 12-dione, 1,3,5-Jtrinitroben2ene;and 9-dicyanomethylene-2,4,7-trinitrofiuorene.

Other typical Lewis Acids include quinones, such as p-benzo-quinone,2,5-dichlorobenzoquinone, 2,6-dichlorobenzoquinone, chloranil,naphthoquinone-( 1,4), 2,3-dichloronaphthoquinone-(1,4), anthraquinone,Z-methylanthraquinone, l,4-dimethyl-anthraquinone,l-chloroanthraquinone, anthraquinoneZ-carboxylic acid,1,5-dichloroanthraquinone, 1 chloro 4 nitro-anthraquinone,phenanthrenequinone, acenaphthenequinone, pyranthrenequinone.chrystenequinone, thio-naphthene-quinone, anthraquinone- 1,8-disulfonicacid and anthraquinOne-Z-aldehyde, triphthaloyl-benzene-aldehydes suchas bromal, 4-nitrobenzaldehyde, 2,6-dichlorobenzaledehyde-2,ethoxy-l-naphthaldehyde, anthracene-9-aldehyde, pyr'ene-B-aldehyde,oxindole-3-aldehyde, pyridine+2,6-dialdehyde, biphenyl-4-aldehyde;organic phosphonic acids such as 4-chloro-3-nitrobenzene-phosphonicacid; nitrophenols, such as 4-nitrophenol, and picric acid; acidanhydrides, for example, acetic-anhydride, succinic anhydride, maleicanhydride, phthalic anhydride, tetrachlorophthalic anhydride,perylene-3,4,9,lO-tetracarboxylic acid andchrysene-2,3,S,9-tetracarboxylic anhydride, di-bromo maleic acidanhydride; metal-halides of the metals and metalloids of the groups 18,II through to group VIII of the periodical system, for example: aluminumchloride, zinc chloride, ferric chloride, tin tetrachloride (stannicchloride), arsenic trichloride, stannous chloride, antimonypentachloride, magnesium chloride, magnesium bromide, calcium bromide,calcium iodide, strontium bromide, chromic bromide, manganous chloride,cobaltous chloride, cobaltic chloride, cupric bromide, ceric chloride,thorium chloride, arsenic triiodide; boron halide compounds for example:boron trifiuoride, and boron trichloride, and ketones, such asacetophenone, benzophenone, 2-acetyl-naphthalene, benzil, benzoin, 5-benzoyl acenaphthene, biacene-dione, S-acetyI-anthracene,9-benzoyl-anthracene, 4-(4-dimethylamino-cinnamoyl) -1- acetylbenzene,acetoacetic acid anilide, indandione-(l,3), (l-3-diketo-hydrindene),acenaphthene quinone-dichloride, anisil, 2,2-pyridil and furil.

Additional Lewis Acids are mineral acids such as the hydrogen halides,sulphuric acid and phosphoric acid; organic carboxylic acids, such asacetic acid and the substitution products thereof, monochloro-aceticacid, dichloroacetic acid, trichloro-acetic acid, phenylacetic acid, and6-methyl-coumarinylacetic acid (4); maleic acid, cinnamic acid, benzoicacid, l-(4-diethyl-amino-benzoyl)benzene- Z-carboxylic acid, phthalicacid, and tetra-chlorophthalic acid,alpha-beta-dibromo-beta-formyl-acrylic acid (mucobromic acid),dibromo-maleic acid, 2-bromo-benzoic acid, gallic acid,3-nitro-2-hydroxyl-l-benzoic acid, Z-nitro phenoxy-acetic acid,2-nitro-benzoic acid, 3-nitro-benzoic acid, 4-nitro-benzoic acid,3-nitro-4-ethoxy-benzoic acid, 2-chloro-4-nitro-1-benzoic acid,2-chloro-4-nitro-l-benzoic acid,

3-nitro-4-'nethoxy-benzoic acid, 4-nitro-l-methyl-benzoic' acid,Z-chloro-S-nitro-l-benzoic acid, 3-chloro6-nitro-1- benzoic acid,4-chloro-3-nitro-l-benzoic acid, 5-chloro-3- nitro-2-hydroxy-benzoicacid, 4-chloro-2-hydroxybenzoic acid, 2,4-dinitro-1-benzoic acid,2-bromo-5-nitro-benzoic acid, 4-chlorophenyl-acetic acid,2-chloro-cinnamic acid, Z-cyano-cinnamic acid, 2,4-dichlorobenzoic acid,3,5-dinitro-benzoic, 3,5-dinitrosalicylic acid, malcnic acid, mucicacid, acetosalicylic acid, benzilic acid, butane-tetracarboxylic acid,citric acid, cyano-acetic acid, cyclo-hexane-dicarboxylic acid,cyclo-hexene-carboxylic acid, 9,10-dichloro-stearic acid, fumaric acid,itaconic acid, levulinic acid (levulic acid), malic acid, succinic acid,alpha-bromostearic acid, citraconic acid, dibromo-succinic acid, pyrene-2,3,7,8-tetra-carboxylic acid, tartaric acid; organic sulphonic acidssuch as 4-toluene sulphonic acid, and benzene sulphonic acids,2,4-dinitro l-methyl benzene dsulphonic acid2,6-dinitro+l-hydroxy-benzene-4-sulphonic acid, 2-nitro-l-hydroxy-benzene-4-sulphonic acid,4-nitro-1-hydroxy-benzene-5-sulphonic acid,6-nitro-4-methyl-1-hydroxy-benzene-2-sulphonic acid,4-chloro-l-hydroxy-benzene-3-sulphonic acid,2-chloro-3-nitro-l-methyl-benzene- 5-sulph0nic acid and2-chloro-l-methyl-benzenet-sulphonic acid.

The following examples will further define the present invention. Partsand percentages are by Weight unless otherwise indicated. The examplesbelow should be considered to illustrate various preferred embodimentsof the present invention.

In each example, the substance to be evaluated is coated from solutionby suitable means onto a conductive substrate and dried. The coatedplate is connected to ground and the layer is electrically charged inthe dark by a corona discharge device (as described by Carlson in US.Patent 2,588,699) to saturation potential using a needlepoint scorotronpowered by a high voltage power supply manufactured by High Volt PowerSupply Company, Condenser Products Division, Model PS101M operat ing at7 kilovolts while maintaining the grid potential at 0.9 kilovolt using aKepco, Incorporated regulated D.C. supply (0.1500 volts). Charging timeis seconds.

The electrostatic potential due to the charge is then measured with atransparent electrometer probe Without touching the layer or affectingthe charge. The signal generated in the probe by the charged layer isamplified and fed into a Mosely Autograf recorder, Model 680. The graphdirectly plotted by the recorder indicates the magnitude of the chargeon the layer and rate of decay of the charge with time. After a periodof about 15 seconds, the layer is illuminated by shining light onto thelayer through the transparent probe using an American Optical Spencemicroscope illuminator having a GE. 1493 medical type incandescent lampoperating at 2800 K. color temperature. The illumination level ismeasured with a Weston Illumination Meter, Model No. 756, and isrecorded in the table. The light discharge rate is measured for a periodof 15 seconds or until a steady residual potential is reached. Theillumination level in each example is about 60 foot-candles.

The numerical difference in the rate of discharge of the charge on thelayer with time in the light minus the rate of discharge of the chargeon the layer in the dark is considered to be a measure of the lightsensitivity of the layer.

A practical test is also made on each material under study which showsphotoconductivity. An electrophotographic image is produced by chargingthe material by corona discharge, exposing the material by projection toa light-and-shadow image and cascade developing the electrostatic latentimage by the method described by Walkup in US. Patent 2,618,551. DetailsEXAMPLE I About 14 parts of an SR82 (a methylphenyl silicone resinavailable from General Electric) solution consisting of about 60% solidsin xylene is mixed with about 40 parts toluene and about partscyclohexanone. To this solution is added about 2 parts of2,4,7-trinitro-9-fluorenone. The solution is coated to about 5 micronsthickness onto a 5 mil aluminum plate (type 1145-Hl9 sold by AluminumCompany of America) by flow coating. The coating is dried, then curedfor about minutes at about 200 C.

A portion of this plate is negatively charged to about 250 volts bymeans of a corona discharge in the manner described by Carlson in US.Patent 2,588,699. The charged plate is then exposed for about 15 secondsby projection using a Simmons Omega D3 Enlarger equipped with an f4.5lens and a tungsten light source operating at 2950 K. color temperature.The light exposure is about 500 footcandle-seconds. The plate is thencascade developed. The developed image is electrostatically transferredto a receiving sheet in the manner described by Schaffert in US Patent2,576,047. The image on the receiving sheet corresponds to the originalprojected image.

The plate is cleaned of residual toner and is reused as by theabove-described process.

Another portion of the above plate is electrometered as previouslydescribed and the results are tabulated in Table 1.

EXAMPLE II A coating solution is prepared as described in Example Iabove, except that about 0.1 part of Brilliant Green Special Dye, atriphenyl methane type dye, Color Index 7 No. 662, available from AlliedChemical Corporation, is added to the solution. The solution is appliedonto an aluminum plate as before and cured in an oven for about 30minutes at about 200 C.

The plate is charged, exposed, and developed as in Example I and theimage is fused onto the plate surface. The image developed on. the platecorresponds to the original.

Another portion of the above plate is electrometered as previouslydescribed and the results tabulated in Table I. As indicated in Table I,the spectral sensitivity and photosensitivity of the plate is improvedby the addition of sensitizing dyes.

EXAMPLE HI A coating solution is prepared as described in Example Iexcept that the 2,4,7-trinitrofluorenone is not included. The solutionis applied onto an aluminum plate as be fore and cured in an oven forabout 30 minutes at about 200 C. The plate is charged, exposed anddeveloped as in Example I. No image is observed on the plate. Anotherportion of the plate is electrometered and the results are tabulated inTable I. As indicated by the table, the plate without the Lewis acid hasno photosensitivity.

EXAMPLE IV About 8 parts of Dow R5061A, a diphenyl type silicone resin,available from Dow Corning, is dissolved in a mixture of about 40 partstoluene and about 20 parts cyclohexanone. To this solution is addedabout 2 parts 2,4,7-trinitrofiuorenone. The solution is applied onto analuminum plate to a thickness of about 5 microns by flow coating. Thecoating is air-dried and then cured at about 200 C. for about 30minutes.

Another portion of the above plate is electrometered as previouslydescribed and the results tabulated in Example I. As can be seen fromthe table, the plate without the Lewis acid has no photosensitivity.

EXAMPLE VII About 2 part of Lucite 2042, an ethyl methacrylate resinmanufactured by E. I. du Pont de Nemours and 5 this resin, when usedalone, has no photosensitivity.

A portion of the above plate is negatively charged to about 300 volts bymeans of corona discharge and exposed for about 15 seconds by projectionusing a Simmons Omega D3 Enlarger equipped with an f4.5 lens and atungsten light source operating at about 2950 K. color temperature. Thetotal exposure is about 500 foot-candle seconds. The plate is thencascade developed, the image is electrostatically transferred to areceiving sheet and is fused. The image on the receiving sheetcorresponds to the original projected image. The plate is cleaned ofresidual toner and is reused by the above described process.

Another portion of the above plate is electrometered as previouslydescribed and the results are given in Table I. As indicated by thetable, this plate has good photosensitivity, with especially highphotosensitivity with negative charging.

EXAMPLE V A coating solution is prepared as described in Example IV'above, except that about 0.1 part of Brilliant Green Special Dye, CI.No. 662, is added to this solution. The mixture is stirred until asolution is achieved and is coated onto an aluminum plate and cured.

The plate is charged, exposed, and developed as in Example IV above andthe image is fused onto the plate surface. The irnage developed on theplate corresponds to the original projected image.

Another portion of the above plate is electrometered as previouslydescribed and the results tabulated in Table I. As can be seen from thetable, the addition of the sensitizing dye produces a very significantincrease in the photosensitivity of the plate.

EXAMPLE VI A coating solution is prepared as in Example IV above, exceptthat the 2,4,7-trinitrofluorenone is omitted from thecoating solution.The mixture is coated onto an aluminum substrate and cured. The plate ischarged, exposed, and developed as in Example IV above. No image isproduced on this plate.

EXAMPLE VIII About 0.2 part of 2,4,7-trinitrofluorenone is added to theresin coating solution prepared as described in Example VII above. Thissolution is applied onto an aluminum sheet to a thickness of about 5microns and dried. The plate is electrometered and the results aretabulated. See Table I.

This plate indicates that the addition of a Lewis acid to an inert resindoes not result in photosensitive response. This indicates thatLewisacids alone are not photosensitive.

EXAMPLE IX A coating solution is prepared as described in Example IVexcept that about 2 parts of 9-dicyanomethylene-2,4,7- trinitrofluoreneis added in place of the 2,4,7-trinitrofluorenone. The mixture isstirred until solution is achieved. The solution is applied onto analuminum plate as before and cured.

The plate is charged, exposed, and developed and the image is fused ontothe plate surface. The image developed on the plate corresponds to theoriginal projected image.

Another portion of the above plate is electrometered as previouslydescribed and the results tabulated in Table I. As seen from the table,the plate has comparable sensitivity when used with a different LewisAcid.

TABLE I Light Dark Residual Sensitivity Imtral d1sehar e dischargepotential (volts/ Example (volts) (volts; (volts! after 15 f. 0. sec.)

sec.) sec.) sec. (v.)

III 3. 6 3. 6 90 0 4. 7 4. 7 I10 0 V +240 58. 8 2. 3 115 94. 2 210 64. 0Trace 100 106. 7

VII +460 4. 4 4. 4 394 0 -500 5. 3 5. 3 420 0 VIII +420 0. 0 0.0 420 0450 0. 0 0. 0 450 0 Although specific materials and conditions were setforth in the above examples, these were merely illustrative of thepresent invention. Various other compositions, such as the typicalmaterials listed above and various conditions, where suitable, may besubstituted for those given in the examples with similar results. Forexample, the aromatic silicone resin may be in the form of a continuouscoating, as in the above examples, or in the form of a sponge orfoam-like layer. The photoconductive composition of this invention mayhave other materials mixed therewith to enhance, sensitize, synergize'or otherwise modify the photoconductive properties of the composition.

Many other modifications of the present invention will occur to thoseskilled in the art upon a reading of this disclosure. These are intendedto be encompassed within the spirit of this invention.

What is claimed is:

1. A photoconductive charge transfer complex material comprising amixture of a Lewis acid and an aromatic silicone resin, saidphotoconductive charge transfer complex material having at least one newabsorption band within a range of from about 3200 to about 7500 angstromunits.

2. The photoconductive material of claim 1 comprising from about 1 toabout 100 parts of said resin for one part Lewis acid.

3. The photoconductive charge transfer complex material of claim 1wherein said Lewis acid is selected from at least one member of thegroup consisting of 2,4,7-trinitro-9-fiuorenone, tetrachlorophthalicanhydride, chloranil, picric acid, benz(a)anthracene-ZlZ-diOne,1,3,5-trinitrobenzene, and 9-dicyanomethylene-2,4,7-trinitrofluor ene.

4. The photoconductive charge transfer complex material of claim 3wherein said Lewis acid is 2,4,7-trinitro- 9-fluorenone.

5. A photoconductive charge transfer complex material comprising amixture of a Lewis acid and an aromatic silicone resin having thegeneral formula:

wherein:

each R is selected from the group consisting of aryl and alkyl radicals,at least one R being an aryl radical; and n is a positive integer havinga value of at least two; said photoconductive charge transfer complexmaterial having at least one new absorption band within a range of fromabout 3200 to about 7500 angstrom units.

6. The photoconductive material of claim 5 comprising from about 1 to100 parts by weight of said resin for every one part Lewis acid.

7. A process for producing a photoconductive charge transfer complexmaterial which comprises mixing an arcmatic silicone resin and a Lewisacid, said photoconductive charge transfer complex material having atleast one new absorption band within a range of from about 3200 to about7500 angstrom units.

8. The process as disclosed in claim 7 wherein said Lewis acid isselected from at least one member of the group consisting of2,4,7-trinitro-9-fiuorenone, tetrachlorophthalic anhydride, chloranil,picric acid, benz(a)anthracene-7,l2-di0ne, 1,3,5-trinitrobenzene, and9-dicyanomethylene2,4,7-trinitrofluorene.

9. The process as disclosed in claim 8 wherein said Lewis acid is2,4,7-trinitro-9-fluorenone.

10. A process for the preparation of a photoconductive charge transfercomplex material comprising mixing a Lewis acid and an aromatic siliconeresin having the general formula:

wherein:

each R is selected from the group consisting of aryl and alkyl radicals,at least one R being an aryl radical; and n is a positive integer havinga value of at least 2; said photoconductive charge transfer complexmaterial having at least one new absorption band within a range of fromabout 3200 to about 7500 angstrom units.

11. The process of claim 10 wherein from about 1 to about parts byweight of resin are mixed with every one part of Lewis acid.

12. An electrophotographic plate comprising a support substrate havingfixed to the surface thereof a photoconductive charge transfer complexmaterial comprising a mixture of a Lewis acid and an aromatic siliconeresin, said photoconductive charge transfer complex material having atleast one new absorption band within a range of from about 3200 to about7500 angstrom units.

13. The electrophotographic plate of claim 12 wherein said aromaticsilicone resin has the general formula:

[0SiO-Sii-] wherein:

each R is selected from the group consisting of aryl and alkyl radicals,at least one R being an aryl radical; and n is a positive integer havinga value of at least 2.

14. The electrophotographic plate of claim 13 wherein said chargetransfer complex material comprises from about 1 to about 100 parts byweight of said resin for every one part of Lewis acid.

15. The electrophotographic plate of claim 12 wherein said Lewis acid isselected from at least one member of the group consisting of2,4,7-trinitro-9-fluorenone, tetrachlorophthalic anhydride, chloranil,picric acid, benz(a)- anthracene-7,12-dione, 1,3,5-trinitrobenzene, and9-dicyanomethylene-Z,4,7-trinitrofluorene.

16. The plate as disclosed in claim 15 wherein said Lewis acid comprises2,4,7-trinitro-9-flu0renone.

17. A process for forming a latent electrostatic charge pattern whichcomprises uniformly electrostatically charging a photoconductive layer,said layer comprising a photoconductive charge transfer complex materialcomprising a mixture of a Lewis acid and an aromatic silicone resin,said charge transfer complex material having at least one new absorptionband within a range of from about 3200 to about 7500 angstrom units, andexposing said photoconductive layer to a pattern of activatingelectromagnetic radiation to produce said charge pattern.

18. The process as disclosed in claim 17 wherein said aromatic siliconeresin comprises the general formula:

wherein:

each R is selected from the group consisting of aryl and alkyl radicals,at least one R being an aryl radical; and n is a positive integer havinga value of at least 2.

19. The process as disclosed in claim 18 wherein said Lewis acid isselected from at least one member of the group consisting of2,4,7-trinitro-9-fluorenone, tetrachlorophthalic anhydride, chloranil,picric acid, benz(a)anthracene-7,l2-dione, 1,3,5-trinitrobenzene, and9-dicyanomethylene-2,4,7-trinitrofiuorene.

20. The process as disclosed in claim 19 wherein said Lewis acidcomprises 2,4,7-trinitro-9-fiuorenone.

21. An electrophotographic imaging process which comprises forming anelectrostatic latent image on the surface of a photoconductive layer,said layer comprising a photoconductive charge transfer complex whichcomprises a mixture of a Lewis acid and an aromatic silicone resin, saidphotoconductive charge transfer complex having at least one newabsorption band within a range of from about 3200 to about 7500 angstromunits and developing said image with electroscopic marking particles.

22. The process as disclosed in claim 21 whereby the steps of forming anelectrostatic latent image and developing said image are repeated atleast more than one time.

11 w .12 23. The process as disclosed in claim-21 wherein said Lewisacid i s selected from at least one member of the aromatic'siliconeresin has the general formula: group consisting of2,4,7-trinitrofluorenone, tetrachloro- I phthalic anhydride, chloranil,picrie acid, benz(a)anthra- R R I cene-7,l2-dione, 1,3,5-trinitrobenzeneand 9-dicyanometh- [O O l 1 U 5 ylene-Z,4,7-trinitrofiuorene..

I I References Cited UNITED STATES PATENTS wherein:

ch R is selected from the group consisting of r l 3,287,120 11/1966Hoegl 96-1.5

and alkyl radicals, at least one R being an aryl radical; 10 JOSEPH RLIBERM AN Primary Examiner and n is a positive integer having a valueof-at least 2. 24. The process as disclosed in claim 23 wherein saidE-VAN HORN, Assistant Examiner-

